Method of forming multifiber structure



Jan. 28, 1964 w. P. BAZINET, JR 3,

METHOD OF FORM ING MULTIFIBER STRUCTURE Lan 9a 6 INVENTOB wnnzao P aazmegm. 68 BY HTTORNEY United States Patent 3,119,678 METHOD OF FORMING MULTIFIBER TRUCTURE Wilfred P. Bazinet, Jr., Webster, Mass assignor to American Optical Company, Southbridge, Mass, a voluntary association of Massachusetts Filed Nov. 18, 1960, Ser. No. 70,195 4 Claims. (Ci. 65-2) This invention relates to light-conducting structures formed of optical fiber-like elements and has particular reference to a fiber optical structure of the type embodying an integration of a plurality of individual lightconducting fiber-like elements secured together in sideby-side relation with each other and novel method of making the same.

In the manufacture of fiber optical light-conducting articles such as face plates or the like wherein literally thousands and often times millions of extremely small light-conducting fiber-like elements are required to be all bundled and secured together in relatively accurate parallel side-by-side relation, it has been a practice to initially form multifibers or like structures which are subsequently bundled and secured together to comprise the final article. As termed herein, a multifiber would embody a compact grouping of a plurality of individual lightconducting fiber-like elements securely fastened together along their adjoining side edges and together, as a unit, being generally of such a length and cross-sectional size as to be considered fiber-like in character. Such multifibers might range in overall cross-sectional size from only a few to several thousandths of an inch in diameter wherein the smaller multifibers might embody light-conducting elements each of only a fraction of a thousandth of an inch in diameter and the larger multifibers might contain lightconducting elements having diameters of one or more thousandths of an inch. It is also pointed out that reference herein to a multifiber structure is intended to include compact and fused together groups of fiber-like elements which resemble multifibers of the above-mentioned character but are considerably larger in size and are of a rigid nature with the fused together fiber-like elements thereof being of individual sizes ranging from fractions of a thousandths of an inch to many thousandths of an inch in thickness.

By following the technique of initially forming multifibers which are subsequently assembled together to construct an article such as a face plate or the like, it can be seen that one avoids the diflicult costly and often next to impossible task of drawing and handling super fine individual light-conducting elements having the minuteness of size required in the structure of the ultimate article. That is, any desired minuteness of fiber element cross-sectional size, preferably no smaller than the wave length of light can be achieved by the practice of drawing multifibers wherein the elements thereof which are initially of a convenient size to handle are assembled together and, as a group, drawn down to a considerably reduced dimension. If, with a single draw, the desired minuteness in cross-sectional size of the individual elements in the resultant multifiber is not achieved, the multifiber can then be cut to predetermined lengths and reassembled to be again drawn down, and so on over again, a number of times until a desired final dimension of the individual elements in the final multifiber is achieved.

While the technique of fabricating articles of the abovementioned character through the use of multifibers has avoided the problems of making and handling super-fine fiber-like elements, the inherent shortcomings of conventional techniques used in the formation of the multifibers themselves has left much to be desired in this field.

In this respect, and because of the fact that a bundle 3,119,678 Patented Jan. 28, 1%64 p ce of unattached fiber-like elements when drawn will tend to attenuate individually and generally remain unattached after drawing, it has, heretofore, been necessary to prefuse the elements together before drawing or to encase the fiber-like elements in a glass tube which is drawn with the fibers or to provide relatively complicated expensive and ungainly arrangements of equipment for holding or forcing the fiber elements together during the drawing thereof.

The expenditures required for equipment and/or time spent in preparing a fiber assembly for drawing a multifiber therefrom in accordance with present-day techniques are undesirable and inconsistent with the strive for economy Without sacrifice of product quality in the fiber optical field wherein it is essential to minimize fabrication costs in order to render the end products economically attractive for commercial use.

This invention obviates the above-mentioned and other drawbacks relating more particularly to the manufacture of multifiber optical elements and minimizes the number of operations required in their fabrication with the result of a substantial saving in manufacturing time and expenditures and without sacrifice of product quality.

Accordingly, it is a principal object of the present invention to provide a unique assembly of fiber optical elements from which a multifiber can be formed and to provide a simple, reliable and economical method for constructing said assembly and forming a multifiber therefrom.

Another object is to provide simple and efiiciently functioning means and method for initially securing a group of fiber elements together in tight interfitting sideby-side relation and for retaining said relationship throughout the operation of drawing said group of fiber elements as a unit to a desired reduced cross-sectional size and with the opposite end faces of the fiber elements substantially identically geometrically patterned.

Another object is to provide securing means of the above character which is completely removable from said group of fiber elements and which in accordance with the present invention is progressively removed from the area adjacent which said group of fibers is heated and drawn during the forming of a multifiber therefrom.

Another object is to provide by the employment of removable securing means of the above character, a finished multifiber consisting of only the initial fiber elements in their attenuated and fused together state as a result of the drawing thereof and completely free of outer surrounding envelopes or other supporting parts such as have been common to prior practices.

Another object is to provide a tight bundle of unattached fiber elements of the above character so arranged by the firmness of the securing means as to permit the evacuation of air or gases endwise from between said elements to render the interfacial areas of the resultant multifiber which is drawn therefrom substantially bubble free and perfectly formed. 7

Another object is to provide, by the action of said vacuum upon the heat softened areas of the fiber elements of said bundle, the additional feature of a pulling or the urging of said fiber elements inwardly and firmly toward each other to assure optimum fusion of their adjoining surface areas and further by said pulling action of said vacuum allowing the use of lower fusing and drawing temperatures than otherwise would be required.

Other objects and advantages of the invention will become readily apparent from the following description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevational view of an assembly of optical fiber elements formed in accordance with the invention;

FIG. 2 is an enlarged cross-sectional view taken on line 2-2 of FIG. 1 looking in the direction indicated by the arrows;

FIG. 3 is a partially cross-sectioned diagrammatic illustration of means and method in accordance with one aspect of the invention for drawing said assembly of fiber elements into a multifiber;

FIG. 4 is an enlarged cross-sectional view taken along line 4-4 of FIG. 3 looking in the direction of the arrows;

FIG. 5 is a partially cross-sectioned diagrammatic illustration of a modification of the invention;

FIG. 6 is a cross-sectional view taken on line 66 of FIG. 5 looking in the direction indicated by the arrows;

FIG. 7 is a View similar to FIG. 6 illustrating a further modification of the invention; and

FIGS. 8 and 9 are diagrammatic partially cross-sectioned views similar to FIG. 3 illustrating a still further modification of the invention.

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, it will be seen that, in accordance with the invention, a multifiber 10 (see FIGS. 3 and 4) is formed by bundling a plurality of fiber elements 12 together as shown in FIG. 1, for example, and heating and drawing the resultant bundle 14 endwise as shown in FIG. 3 to a reduced cross-sectional size equal to that desired of the multifibers 10.

The fiber elements 12 are preferably of the well-known clad or individually light-insulated type each embodying a core part of material such as optical flint glass or the like having a relatively high index of refraction surrounded by a relatively thin cladding of crown or soda lime glass or material of a similar nature having an index of refraction lower than that of said core part. In the usual manner of fabricating such fiber elements, materials which are to comprise the core and cladding parts thereof are selected to have indices of refraction of such relative values as to provide the ultimate fiber elements 12 each with a maximum light-aperture or acceptance angle within which light entering one end thereof will be substantially totally internally reflected adjacent the interface between the said core and cladding parts and thereby transferred through the elements from end-to-end with a minmimum loss in intensity. In this way, the cladding part functions to light-insulate one adjacent fiber element 12 of the bundle 14 or the resultant multifiber 10 from another fiber element thereof so as to substantially obviate the effects of cross-talk (the passing of light from one fiber element to another). As it is Well known in the field of fiber optics, cross-talk is extremely detrimental particularly in instances where a structure formed of many optical fibers is intended for use as means to receive and transfer optical images from one location to another by conducting adjacent elements of an image each through a particular fiber. Cross-talk intennixes these image elements and thereby deteriorates the overall transferred image.

The multifiber 10 of the invention is intended for use in the ultimate construction of devices for transferring optical images or it may be employed in the construction of devices used simply to conduct non-image forming light from one location .to another. It should also be understood that the multifiber itself and as a single unit may be used as means either to transfer optical images or light which is not in the form of an image.

A typical fiber element 12 construction suitable for the formation of the multifiber structure 10 of the invention might embody, for example, a core part of fiint glass having an index of refraction of approximately 1.62 with a cladding of soda lime glass having an index of refraction of approximately 1.52. A suitable cladding thickness might be in the neighborhood of one-tenth the overall diameter of the fiber itself. Such fiber elements 12 may be formed by placing a relatively large rod of the higher index glass within a relatively close fitting tube of the lower index glass with said rod and tube having relative thicknesses proportionate to those desired of the respective core and cladding parts desired of the elements 12 and heating and drawing the rod and tube assembly down to the ultimate size desired of the elements 12.

As mentioned above, the present invention provides means and method for forming a multifiber which ultimately embodies many super fine accurately aligned individuallly functioning light-conducting channels formed of the fiber elements 12 without, at any time, having to handle excessively fine and unmanageable'fiber elements. To this end, the original fiber elements 12 are selected to be of a cross-sectional size such as 40 to thousandths of an inch in diameter, for example, which renders them easily handled and simple to bundle or handpack together in accurate side-by-side aligned relation with each other in the form of the bundle 14 wherein the opposite end faces of the fiber elements of the bundle 14 are substantially identically geometrically patterned.

The fiber elements 12 are preferably uniform in shape throughout their length and circular in cross-section as illustrated (FIG. 2) or of any other shape such as to be, when bundled tightly, intimately interfitted so as to effectively produce a substantially continuous line-like contact along their adjacent edges. This provides somewhat of an air-tight seal between the adjacent fiber elements 12 and an interstice 16 (see FIG. 2) extending from end-toend throughout the length of the bundle 14 between sub stantially each and every one of the fiber elements 12.

After being handpacked or otherwise so assembled, the fiber elements 12 which comprise the bundle 14 are bound together with tightly applied ties 18 at spaced points along the length of the bundle 14. The ties 18 are preferably formed of woven or stranded fiber glass such as pyrex or the like which will characteristically withstand relatively high temperatures. A bundle 14 having a diameter of approximately one inch and formed of fiber elements 12 of the above-mentioned cross-sectional size might, for example, be tied at points approximately from Mt to /z of an inch apart along its length. The exact spacing of the ties 18 is not critical but should be such as to produce and retain the above-mentioned firm line contact between each of the adjacent fiber elements 12 with said fibers being aligned throughout substantially the entire length of the bundle 14.

Before or after the tying of the bundle 14, a tubular member 20 of glass, metal or any other suitable material which will withstand relatively high temperatures is placed over one end of the bundle (see FIGS. 1 and 2) and secured thereto either with a suitable tape or preferably with a sealing agent 26 such as an inorganic silicate base cement of other suitable sealing means which will withstand relatively high temperatures.

It is pointed out that the assembly 14 may be made by initially passing the fiber elements 12 as a group endwise through the tubular member 20 in a direction from the end 22 toward and out through the end 24. This will automatically provide the bundle 14 with an outer contour shape substantially contrageneric to that of the inner peripheral shape of the member 20 which may be circul'ar as shown or alternatively might be hexagonal or of any other desired configuration. In order to retain the shape of the bundle 14, the ties 18 may be applied progressively as the fibers 12 are forced through the end 24 of the member 20 and when the major portion of the length of the bundle has been tied as shown in FIG. 1, the member 20 would be cemented or otherwise attached thereto as mentioned above.

When the assembly 14- has been tied tightly and attached to the tubular member Zll, it is suspended vertically as shown in FIG. 3 so as to be in approximately coaxial relation with an annular heating element 28 which, in the present instance, will be considered to be stationary. It will become apparent, however, that in accordance with the method of the invention, the heating element 28 might be arranged to be adjustable and movable vertically in a direction along its axis.

The uppermost end of the bundle 14 is clamped within a holder 30 which preferably surrounds the tubular meanber 20 as shown in FIG. 3 and is held in place with a set screw or the like 32. The holder 34} is provided with w internally threaded portion 34 through which an axially rotatable lead screw 36 extends in threaded relation therewith. The lead screw 36 is journaled adjacent both of its ends in stationary bearing supports 33 and is rotated by means of a pulley and belt arrangement 46 or any other suitable drive means which is motivated by an electric motor 42 or the like. Being disposed vertically and substantially parallel to the bundle 14, the lead screw 36, will, when rotated in the proper direction, cause the bundle 14 to lower into and through the heating element 28.

The open end of the tubular member 2% is provided with a stopper 44 or any suitable closure member through which a vacuum line 46 is extended into the area between the adjacent end 48 of the bundle l4 and the stopper 44.

With the arrangement of FIG. 3, the multifiber is drawn from the bundle 14 as follows:

The initially depending end of the bundle 14 which is shown by reference numeral 56- in FIG. 1 is lowered into the area surrounded by the heating element 28, which area will be referred to hereinafter as the heating zone 52. A vacuum is drawn through the interstices 16 between the fiber elements 12 by means of the vacuum line 46 and because of the fact that the fiber elements 12 are tightly bundled and tied as described above so that substantially all of the fiber elements 12 including the outermost thereof in the bundle 14 are in firrn side-by-side relation, the line contact therebetween will prowide a relatively tight seal to close oif the interstices 1.6 so that, while some leak-age of air therethrough might take place, a relatively high and effective vacuum will be produced which, in addition to removing air and gases from said interstices will tend to pull the fiber elements inwardly toward each other so as to further tighten the relationship or the fiber elements 12.

Upon entering the heating zone 52 which according to the above-described glasses is hemed by the element 23 to a suitable glass drawing temperature of approximately 1400 F. to 1500 F., the glasses of the fiber elements 12 will become softened only to a state whereby they will yield to the pull of the vacuum with the effect of becoming further compacted and tightly interfitted. It is to be understood that other temperatures of heating will be required depending upon the nature of the glasses used for the combined cores and claddings.

It is pointed out that as the end 59 of the bundle enters the heating zone and immediately prior to the point where the location of the first tie .18 enters said zone, the first tie is removed as shown by 18' in FIG. 3. The ties it; are preferably initially fastened with a slip knot or how knot so that they can be quickly and easily removed by a pull on one loose end thereof.

At the point where the ties 18 are removed, the adjacent areas of the glasses or the fiber elements 12 will be at such a softened state as to yield to the pull of the vacuum and be held tightly together thereby. At the same time, because of the fact that they are approaching the glass drawing temperature, the fiber elements 12 will begin to wet each other and initiate the resultant fused joinder therebetween which, as it will become apparent, is assisted by the action of pulling or drawing of the multifiber 10 of a reduced size therefrom.

When the initially depending end 50 of the bundle 14 is heated to the above-mentioned suitable drawing temperature, it is baited by passing a glass baiting rod (not shown) upwardly through the heating zone 52, from underneath, into engagement with the said end 59 of the bundle. The baiting rod is selected to have substantially the same melting temperature as that of the fiber elements 12 and will fuse thereto. When fused to the ends of the fiber elements 112, the baiting rod is pulled downwardly to carry the entire unit of the fiber elements with it and thereby initiating the drawing of the multifiber 10.

The drawing of the multifiber 10 is then continued by attaching the same to a motor-driven drum 56 or any suitable means for continuing the pull.

The drum 56 which has been shown for purposes of illustration only, is rotatably driven preferably by a constant speed motor 58 through a conventional gearing arrangement 60 adapted to provide a constant precontrolled rate of pull upon the multifiber 10.

As the multifiber 10 is drawn, the motor 42 is simultaneously operated to lower the bundle 14 endwise into the heating zone 52 at a rate in accordance with the rate of removal of material from the bundle 14 resulting from the drawing of the multifiber 10 therefrom.

It is pointed out that as each successive tie 18 is about to enter the heating zone 52, it is removed as described above with relation to the tie 18'.

The drawing rate produced by the motor-driven drum 5% is controlled in accordance with the ultimate size desired of the multifiber 10 (faster drawing rates produce smaller multifibers) and the rate of lowering of the bundle and temperature in the heating zone 52 are also cooperatively controlled in accordance with the drawing rate in the usual manner common to fiber drawing operations to produce the end result of a uniformly dimensioned continuous multifiber 10.

It is pointed out that the fiber elements 12, when drawn to the reduced cross-sectional size shown as 12' in FIG. 4 will inherently retain substantially the same proportional relationship of core to cladding thickness as that of the original elements 12 (FIGS. 1, 2 and 3) and the general outer contour shape of the multifiber 10 will be substantially identical to that of the bundle 14. That is, by drawing a circular bundle 14, a circular multifiber it) (FIG. 4) will result whereas if the bundle 14 were hexagonal for example, the resultant multifiber would be substantially hexagonal in cross-sectional shape. These shape characteristics of the multifiber are inherent to fiber drawing operations Where proper temperatures and rates of draw are practiced.

In addition to the above-mentioned shape and size characteristics of the multifiber 10, each of its fiber elements 12 become compacted and squeezed together by the combined action of the pull of the vacuum and the drawing action of the drum 56 and take on a cross-sectional shape such as to close off the voids or interstices 16 therebetween and become completely and securely as well as cleanly fused and sealed together throughout all of their adiacent side surface areas.

It should be understood that, in accordance with this invention which features the drawing of a multifiber directly from a bundle of unattached fiber elements such as 12 through the bundle, a relatively large multifiber structure may be formed which is similar in all respects to the fiber element 1% This, of course, would be accomplished by applying only a slight draw to the bundle 14 so as to reduce its size only sufficiently to bring about the above-mentioned compacting and sealed fusing together of the elements 12 thereof. Also, tapered multifiber elements can be formed from the bundle 14 by controlling the related rates at which the bundle 14 is lowered and drawn.

In all instances, however, the resultant multifiber structure or multifiber it, which is shown for illustration purposes, will be free of any outer glass supporting shells or other binding means which have been common to some prior practices and will consist of nothing more than the integrated composite fused arrangement of the individual elements 12 (see FIG. 4). That is, all ties 18 or other bundling and holding arrangements which will be discussed hereinafter are removed immediately prior to the fusion and drawing of the bundle 14.

It should be also understood that, if it is desired to reduce the cross-sectional size of the fiber elements 12' (FIG. 4) still further, the multifiber 10 can be cut to predetermined lengths and the lengths reassembled to form a bundle thereof which simulates the bundle 14 shown in FIG. 1. With the reassembled multifiber lengths, the above-described bundling and drawing operation would be repeated. The operations of cutting, re-bundling, and redrawing can be repeated a number of times suificient to produce a multifiber structure having the desired minuteness of individual element size and the proper fusing and/or air sealing of said multifibers with each other.

In FIG. 5, there is shown a modification of the invention wherein automatically functioning means is provided to remove the ties 18 from the bundle 14 at the proper time and progressively as the bundle 14 is lowered into the heating zone 52. This tie removal arrangement embodies a knife like cutter 62 (see FIG. 5) which is fixed to the stationary support 64 for the heating element 28. The cutter must be formed of a material able to withstand high temperatures such as those produced in the area adjacent the heating element and may be formed either of a suitable metal or ceramic or the like having a sharpened leading edge directed upwardly and riding against or at least immediately adjacent the fiber bundle 14.

In order to protect the cutter 62 from the intense heat produced in the zone 52, a shield 66 of heat resistant glass, mica or other material is placed over the heating zone 52 in such manner as to closely surround the bundle 14 as it is lowered into the heating zone 52. Further, with a view to protecting the cutter 62 from excessive temperatures and to assist in holding the fiber elements 12 tightly together after the ties 18 are cut, a ring-like member 68 is placed over the shield 66. The member 68 is provided with an internal opening 70 of such size and shape (see FIGS. 5 and 6) as to intimately but slidingly receive the fiber bundle 14 after the ties 18 are cut therefrom. Thus, it can be seen that when the tied fiber bundle 14 is lowered during the drawing of a multifiber therefrom, its ties 18, upon approaching the edge 64 of the cutter 62 are cut and will fall away from the bundle as shown at 18" and the fiber elements 12 will immediately thereafter enter and are held together by the member 68.

The member 68 is preferably formed of a refractory material or the like which is highly resistant to high temperatures and which will remain dimensionally stable and not stick to the glass bundle 14 or in any Way deter the movement of said glass bundle therethrough. Moreover, the member 68 is preformed to have an internal opening of a particular shape substantially contrageneric to that of the overall outer contour shape of the bundle 14. In this respect, it will be noted that if the bundle 14 were hexagonal as shown in FIG. 7 by the reference number 14' a ring-like member of the type shown by reference numeral 68' would be used to replace the member 68 of FIGS. 5 and 6. The member 68 accordingly has a hexagonal opening 70' therein of a contour size and shape substantially equal to that of the fiber bundle 14'.

In FIGS. 8 and 9, there is shown a still further modification of the invention wherein a spring-like member 72 formed of a high temperature resisting material is used to support the fiber elements 74 of a bundle 76 thereof in place of the above-described ties 18.

The bundle 76 being formed of fiber elements 74 which are identical in character to the above-described elements 12 is initially inserted into the spring-like member 72 which is controlled to be of a size such as to tightly fit about the bundle 76 and hold the fiber elements 74 thereof tightly and securely in such a side-by-side aligned relationship as to permit the drawing of at least a partial vacuum in the interstices between the fiber elements 74. The spring-like member 72 is, however, controlled in size and tightness of fit relative to the bundle 76 size as to permit each of its convolutes to slide along the bundle when the member 72 is compressed. That is, when one end is pushed toward the other end thereof. This tightness of fit on the bundle 76, however, is controlled to be such as to prevent translation of the compressing force from one convolution to another as would be the case if a member such as 72 were loosely fitted on the bundle 76. That is, as one end of the spring-like member is forced toward its opposite end, the first convolution will move up to engage the next convolution and in turn move up to the third convolution and so on. The force on the first convolution will not be translated throughout the length of the member 72. This action will become more apparent from the following description of the multifiber drawing operation.

The bundle 76 of fiber elements '74 is supported at its uppermost end in a tubular member '78 which is sealed with a stopper or the like 80 having a vacuum line 82 extending therein and the entire assembly is clamped within a vertically movable holder 84 which is operated with a lead screw 86 to lower the bundle 76 endwise substantially axially through a heating element 88. Over the heating element 88, there is placed a ring-like member 90 preferably of the type referred to as 68 in FIGS. 5 and 6 and against which one end 92 of the spring-like member 72 abuts. A collar 94 placed around the bundle 76 and against the depending end of the tubular member 78 is provided as stop means for the opposite end 96 of the spring-like member 72. Thus, the spring-like member 72 is confined between the collar 94 and the ring-like member 90 so that, as the holder 84 is lowered to move the bundle 76 into the area of the heating elements 88, the convolutes of the spring-like member which are rightly fitted on the bundle 76 are carried downwardly with the bundle towards the member 90 and as a result, effectively pile up upon one another as illustrated in FIG. 9. As pointed out above, due to the initial tight fit of the convolutes of the spring-like member upon the bundle, no translation of the resultant compressing force is carried from end to end through the spring-like member and no loosening eifect beyond a point adjacent the ring-like member 90 is produced upon the bundle as a result of the compression or piling up of the convolutes of the springlilre member. Since the convolutes of the spring-like member 72 pile up adjacent the ring-like member 90 which then takes over the support of the bundle 76, the initial alignment and tight fit of the fiber elements 74 is maintained substantially constant throughout the fiber drawing operation and the resultant relatively tight adjoinment of said fiber elements permits the pulling of a vacuum therebetween to evacuate gases, air, dust, dirt and the like and to effect an inwardly directed force upon the fiber bundle in the heat softened area thereof to bring about a substantially perfect fusing together of each and very fiber element 74 at the time of drawing. The multifiber 98 is drawn from the bundle 76 in a manner such as described above with relation to FIGS. 1-7 by practicing proper control of the temperature produced by the heating element 88 and using proper rates of lowering and drawing of the bundle 76.

In all of the above-described cases where a multifiber or multifiber-like structure is drawn, it is pointed out that no prefusing step is required. That is, the multifiber structure is drawn directly from a bundle of initially unattached fiber elements through the use of a vacuum and with removable means holding the bundle together. Furthermore, the resultant multifiber element is entirely free of surrounding glass tubular parts or other structures commonly used heretofor in multifiber construction practices and thereby enables said elements to be regrouped and redrawn in direct fiber to fiber contacting relation with each other.

It is pointed out, that if it is desired to render the bundle substantially completely air or vacuum tight along its side edges in order to efiect a greater than usual pull upon the fiber elements thereof by the above-described vacuum system, the sides of the bundle may be bound with a tape which would normally be removed immediately prior to entering the heating zone of the drawing apparatus. The tape might be of the heat-resisting type which is non-permeable and formed of asbestos Teflon or other known heat-resistant materials or it may be formed of a material which, upon entering the said heating zone, will burn off. This latter arrangement would not require removal of the tape before entering the heating zone. The tape may be used to replace the above-described ties 18 or used along with the ties wherein it would be applied either over or under the ties 18 as desired. Sealing agents other than a tape may also be used to effect a more positive seal about the sides of the bundles 14 or 76. Such an agent would preferably be characterized as to burn when subjected to the above-mentioned fiber drawing temperatures without leaving residue upon the finally formed multifiber. A suitable sealing agent might be a cellulose nitrate or a similarly characterized material which can be applied by painting the fiber bundle therewith or by a dipping operation or in any convenient fashion.

From the foregoing description, it will be seen that simple, efiicient and novel means and method has been provided for accomplishing all of the objects and advantages of the invention. However, it should be apparent that many changes in the details set forth hereinabove may be made without departing from the spirit of the invention as expressed in the accompanying claims.

Having described my invention, I claim:

1. The method of forming a fused multifiber structure comprising bundling a plurality of fiber-like light-conducting elements together in substantially parallel sideby-side engaging relation, said fiber elements having crosssectional shapes of such character as to produce interstices therebetween extending from end-to-end throughout the length of said bundle, applying removable binding means peripherally about the sides of said bundle with such firmness as to position and compressively hold said elements in side-by-side line contact with one another throughout the major portion of the length of said bundle and to provide such an intimate adjoinment along said lines of contact as to effectively prevent any appreciable passage of air through the sides of said bundle, applying zoned heat circumferentially about said bundle adjacent one end thereof of a temperature sufficient to render the materials of said elements suitably viscous for fusing and drawing and to cause corresponding ends of said elements to become heat sealed together, continuously evacuating air and gases from said interstices through the opposite end of said bundle to create a vacuum in said interstices to cause said elements of said bundle to be com pressed further into fused interfitting side-by-side rela tion by atmospheric pressure surrounding said bundle in portions thereof heat-softened by said zone of heat, moving said zone of heat and said bundle one relative to the other at a controlled rate and in such manner as to cause said zone of heat to pass progressively along the length of said bundle from said initially heat sealed end thereof, simultaneously progressively removing said binding means adjacent said zone of heat as the entrance of adjacent portions of said bundle into said zone of heat takes place Without releasing said compressive holding eifect of said binding means throughout remaining portions of the length of said bundle and drawing said bundle endwise from said initially heat sealed end thereof at a controlled rate greater than that of the progression of said zone of heat along said bundle to attenuate said bundle and produce a fused multifiber structure embodying an integral assembly of said fiber elements only.

2. The method of forming a fused fiber optical structure comprising bundling a plurality of fiber-like lightconducting elements together in substantially parallel side-by-side engaging relation, said fiber elements having cross-sectional shapes of such character as to produce interstices therebetween extending from end-to-end throughout the length of said bundle, and each embodying a core part of light-conducting material having a relatively high index of refraction and an integrally related surrounding relatively thin cladding of material having a relatively low index of refraction, applying removable binding means peripherally about the sides of said bundle with such firmness as to position and compressively hold said elements in side-by-side line contact with one another throughout the major portion of the length of said bundle and to provide such an intimate adjoinment along said lines of contact as to elfectively prevent any appreciable passage of air through the sides of said bundle, applying zoned heat circumferentially about said bundle adjacent one end thereof of a temperature sufficient to render the materials of said elements suitably viscous for fusing and drawing and to cause corresponding ends of said elements to become heat sealed together, continuously evacuating air and gases from said interstices through the opposite end of said bundle to create a vacuum in said interstices to cause said elements of said bundle to be compressed further into fused side-by-side relation by atmospheric pressure surrounding said bundle, in portions thereof heat softened by said zone of heat, lowering said bundle endwise at a controlled rate through said zone of heat, simultaneously progressively removing said binding means adjacent said zone of heat prior to the entrance of adjacent portions of said bundle into said zone of heat without releasing said compressive holding effect of said binding means throughout remaining portions of the length of said bundle, and drawing said bundle endwise from said initially heat sealed end thereof at a controlled rate greater than that of said rate at which said bundle is lowered through said zone of heat to attenuate said bundle and produce said fused multifiber structure.

3. The method of forming a fused multifiber structure comprising bundling a plurality of individual fiber-like light-conducting elements together in substantially parallel side-by-side engaging relation, said fiber elements having cross-sectional shapes of such character as to produce interstices therebetween extending from end-to-end throughout the length of said bundle, applying removable ties peripherally about the sides of said bundle at relatively closely spaced intervals along the length thereof with such firmness as to position and compressively hold said elements in side-by-side line contact with one another throughout the major portion of the length of said bundle and to provide such an intimate adjoinment along said lines of contact as to effectively prevent any appreciable passage of air through the sides of said bundle, applying zoned heat circumferentially about said bundle adjacent one end thereof of a temperature sufiicient to render the materials of said elements suitably viscous for fusing and drawing and to cause corresponding ends of said elements to become heat sealed together, continuously evacuating air and gases from said interstices through the opposite end of said bundle to create a vacuum in said interstices to cause said elements of said bundle to be compressed further into fused side-by-side relation by atmospheric pressure surrounding said bundle in portions thereof heat-softened by said zone of heat, moving said zone of heat and said bundle one relative to the other at a controlled rate and in such manner as to cause said zone of heat to pass progressively along the length of said bundle from said initially heat sealed end thereof, simultaneously progressively removing said ties, one at a time, adjacent said zone of heat prior to the entrance of adjacent portions of said bundle into said zone of heat without releasing said compressive holding effect of said ties throughout remaining portions of the length of said bundle, and drawing said bundle endwise from said initially heat sealed end thereof at a controlled rate greater than that of the progression of said zone of heat along the length of said bundle to attenuate said bundle and produce said fused multifiber structure.

4. The method of forming a fused multifiber structure comprising bundling a plurality of individual fiber-like light-conducting elements together in substantially parallel side-by-side engaging relation, said fiber elements having cross-sectional shapes of such character as to produce interstices therebetween extending from end-to-end throughout the length of said bundle, applying removable binding means wrapped helically peripherally about the sides of said bundle with such firmness as to position and compressively hold said elements in side-by-side line contact with one another throughout the major portion of the length of said bundle and to provide such an intimate adjoinment along said lines of contact as to effectively prevent any appreciable passage of air through the sides of said bundle, applying zoned heat circumferentially about said bundle adjacent one end thereof of a temperature sufficient to render the materials of said elements suitably viscous for fusing and drawing and to cause cor-' responding ends of said elements to become heat sealed together, continuously evacuating air and gases from said interstices through the opposite end of said bundle to create a vacuum in said interstices to cause said elements of said bundle to be compressed further into fused sideby-side relation by atmospheric pressure surrounding said bundle in portions thereof heat softened by said zone of heat, moving said zone of heat and said bundle one relative to the other at a controlled rate and in such manner as to cause said zone of heat to pass progressively along the length of said bundle from said initially heat sealed end thereof, simultaneously progressively removing said wrapped binding means adjacent said zone of heat prior to the entrance of adjacent portions of said bundle into said zone of heat without releasing said compressive holding effect of said binding means throughout remaining portions of the length of said bundle and drawing said bundle endwise from said initially heat sealed end thereof at a controlled rate greater than that of the progression of said zone of heat along the length of said bundle to attenuate said bundle and form said fused multifiber structure.

Referenees Cited in the file of this patent UNITED STATES PATENTS 2,484,003 Simison Oct. 4, 1949 2,992,516 Norton July 18, 1961 3,004,368 Hicks Oct. 17, 1961 

1. THE METHOD OF FORMING A FUSED MULTIFIBER STRUCTURE COMPRISING BUNDLING A PLURALITY OF FIBER-LIKE LIGHT-CONDUCTING ELEMENTS TOGETHER IN SUBSTANTIALLY PARALLEL SIDEBY-SIDE ENGAGING RELATION, SAID FIBER ELEMENTS HAVING CROSSSECTIONAL SHAPES OF SUCH CHARACTER AS TO PRODUCE INTERSTICES THEREBETWEEN EXTENDING FROM END-TO-END THROUGHOUT THE LENGTH OF SAID BUNDLE, APPLYING REMOVABLE BINDING MEANS PERIPHERALLY ABOUT THE SIDES OF SAID BUNDLE WITH SUCH FIRMNESS AS TO POSITION AND COMPRESSIVELY HOLD SAID ELEMENTS IN SIDE-BY-SIDE CONTACT WITH ONE ANOTHER THROUGHOUT THE MAJOR PORTION OF THE LENGTH OF SAID BUNDLE AND TO PROVIDE SUCH AN INTIMATE ADJOINMENT ALONG SAID LINES OF CONTACT AS TO EFFECTIVELY PREVENT ANY APPRECIABLE PASSAGE OF AIR THROUGH THE SIDES OF SAID BUNDLE, APPLYING ZONED HEAT CIRCUMFERENTIALLY ABOUT SAID BUNDLE ADJACENT ONE END THEREOF OF A TEMPERATURE SUFFICIENT TO RENDER THE MATERIALS OF SAID ELEMENTS SUITABLY VISCOUS FOR FUSING AND DRAWING AND TO CAUSE CORRESPONDING END S OF SAID ELEMENTS TO BECOME HEAT SEALED TOGETHER, CONTINUOUSLY EVACUATING AIR AND GASES FROM SAID INTERSTICES, THROUGH THE OPPOSITE END OF SAID BUNDLE TO CREATE A VACUUM IN SAID INTERSTICES TO CAUSE SAID ELEMENTS OF SAID BUNDLE TO BE COMPRESSED FURTHER INTO FUSED INTERFITTING SIDE-BY-SIDE RELATION BY ATMOSPHERIC PRESSURE SURROUNDING SAID BUNDLE IN PORTIONS THEREOF HEAT-SOFTENED BY SAID ZONE OF HEAT, MOVING SAID ZONE OF HEAT AND SAID BUNDLE ONE RELATIVE TO THE OTHER AT A CONTROLLED RATE AND IN SUCH MANNER AS TO CAUSE SAID ZONE OF HEAT TO PASS PROGRESSIVELY ALONG THE LENGTH OF SAID BUNDLE FROM SAID INITIALLY HEAT SEALED END THEREOF, 